This invention concerns a process and a machine for the production of a package made up of threads assembled by multidirectional weaving i.e. deposit of thread about a network of rods; and susceptible to serve as a framework in the manufacture of a body made of composite material.
Such frameworks are utilized, after impregnation with a suitable binder and subsequent hardening of the binder, for the purpose of obtaining components capable of withstanding very high mechanical and thermal stresses, for example, those used for the structural components of satellites, re-entry bodies, or rotor hubs for rotary winged aircraft.
A manual process is already known from U.S. Pat. No. 4,218,276 (AVCO), for creating three-dimensional structures, consisting of upwardly pointed vertical and parallel needles, held apart by two reeds arranged at right angles. Over the needle points a layer of fabric is then placed, and against it is pressed a plate equipped with holes corresponding to the needles, the points of which penetrate the fabric which is pressed downwardly by the plate. This operation is repeated by rotating the reeds until the required stack thickness is obtained, after which the stack is removed from the machine. Then, filamentary reinforcements are introduced into the holes made in the stack so as to form a three-dimensional structure. In order to put this process into operation, it is therefore necessary to have available layers of fabric manufactured in advance and trimmed to the dimensions required for each specific product. Moreover, while this U.S. patent proposes the creation of so-called three-dimensional structures in which rigid components such as metallic needles are arranged vertically, it can be seen that such structures cannot be obtained by the simultaneous deposit of threads on those needles. Instead, bonded layers are formed first, after which they are stacked up and then penetrated by the needles.
Likewise known, from U.S. Pat. No. 4,183,232, to the present applicant, is a three-dimensional weaving machine for the production of hollow, rotating woven frames. Into a network of rods, held parallel to the generating lines of the body to be created by means of gratings, there are introduced and woven on a fixed plane, on the one hand, circumferential threads by unwinding in concentric circles parallel threads, and on the other, radial threads by knitting by means of a needle, of a thread in the form of a chain. In this process, the rods can be metal pins which, at the end of the weaving, are removed and replaced, through a lacing arrangement, by threads which provide longitudinal filling.
The process known from U.S. Pat. No. 3,955,602 makes it possible to create pieces of simple geometric shape, such as, essentially, parallelepiped blocks in which the threads deposited on a single plane emerge on either side of a network of vertical pins with an overlap, requiring, on this account, the use of a thread locking device. U.S. Pat. Nos. 3,955,602; 4,183,232 and 4,218,276 discussed above are incorporated here by reference.
In general, the processes according to the prior art require specific tooling for the piece to be made to the extent that the weaving is linked to the separation or pitch of the vertical pins. Consequently, they do not permit rapid and economical changes in the woven pieces.
Moreover, most of the known processes for the creation of woven pieces of three dimensions require the installation of a substantial number of thread bobbins, and consequently, the manipulation of same in order to pass from one piece to another.
Finally, the essential problem to be resolved in the weaving of structures of the type considered lies in the fact that the threads to be introduced in a network of pins or rods must be deposited in such a way that no residual tension will be retained in them.
In fact, the accumulated tensions would finally deform the network and prevent continued production, by shutting down the respective machine, for example. This problem is usually resolved, either empirically, through the skill of the operator, or by the use of pin-holding equipment with introduction of the threads under tension and threading each thread into a needle.